High speed electric machines or high speed, high power electric motors are used in many different applications. For example, high speed, high power electric motors may be utilized in industrial applications to power pumps, fans, blowers, or compressors. High speed, high power electric motors that operate at variable speed are increasingly required in a range of industrial, mining, and drilling activities. Further, the activities often require a high-degree of reliability. In operations such as crude oil pumping from remote global locations where access to pumping stations is difficult and time consuming, reliability of motor operation is necessary to prevent dangerous, costly, and extended outages.
A high-speed, high power electric motor may receive power from a power source. In many applications, the signal that is output from the power source is passed through a power converter prior to being input into the high-speed, high power electric motor. For example, a direct current power signal may be output from the power source and then passed through a direct current to alternating current (“AC”) converter in order to produce an appropriate signal for powering an AC electric motor. Additionally, a power converter may incorporate one or more switches that are selectively actuated in order to produce an appropriate signal for powering an electric motor. These switches may be semiconductor devices such as, for example, thyristors (also referred to as “SCRs,” or “silicon controlled rectifiers”), triacs, power transistors, power metal oxide semiconductor field-effect transistors(referred to as “MOSFETs”), insulated gate bipolar transistors (referred to as “IGBTs”), integrated gate commutated thyristors (referred to as “IGCTs”), and MOS-controlled thyristors (referred to as “MCTs”).
Simple, sturdy, and reliable power converters are requisites for such high-speed, high power motor operations. Converters including multiple, individual components, such as series or parallel semiconductor switches, may have an increased likelihood that any one individual component switch may randomly fail. Adding elements to the converters, such as snubber circuits for semiconductor switches, further increases the number of components that may fail. Thus, it is desirable to arrange a power converter in a simple configuration and to reduce the component count. However, individual components of the power converters should be operated within satisfactory thermal margins and other functional limitations to avoid failures in the simplified converter configurations.
Additionally, for many applications, a high-speed, high power electric motor with a certain power output is required. As the size of the motor is decreased, the same power output may be achieved by increasing the frequency or speed at which the motor rotates. In many cases, the frequency at which the switches are actuated in the power converter is increased to accommodate the increased rotational speed or rotational velocity of the high-speed, high power electric motor. In other words, a higher frequency signal is applied to the motor from the power converter.
Providing a higher frequency input signal to the high-speed, high power electric motor from the power converter, however, may lead to increased heat and total harmonic distortion in the components of the motor. Additionally, increasing the switching frequency of the power converter may lead to a higher amount of switching loss in the power converter.
Accordingly, there exist a need for improved systems and methods for controlling a converter for powering a load.
There is a further need for systems and methods for controlling a converter for powering a load that reduce switching loss and total harmonic distortion in the load.